1. Field of the Invention
The present invention relates to a micro-bubble generating device and a silicon wafer cleaning apparatus comprising the micro-bubble generating device.
2. Background Art
In recent years, in manufacturing semi-conductor LSI using a silicon wafer, wafers having larger diameters and finer processing technology are increasingly needed. Furthermore, problems related to maintaining and enhancing product quality accompanying more complicated fabrication processes and related to production cost reduction, etc. have also become problematic.
Particularly in many fields of semi-conductor LSI manufacturing technology using silicon wafers, a so-called a wet treatment process including treatments by various solutions has become an essential part of the manufacturing process. Important processes among such wet treatment processes are cleaning processes and etching processes, etc. In these wet treatment processes, conventional improvements are mostly directed to selecting a solution type, a density, a treatment temperature, a time frame, etc. (For example, see Tsuyoshi Hattori “New Edition of Cleaning Technology of Silicon Wafer Surface” Realyze Science & Engineering (2000).) However, these conventional technologies were not sufficient to fulfill requirements associated with further fine processing technologies in recent years, the more complicated processes, high cleanliness, and cost reduction. Furthermore, in recent years, treatments by dilute chemical cleaning and chemical-solution-less cleaning, etc. have been desired due to requirements with respect to tightening environmental protection measures and cost reduction of waste liquid treatment.
Use of micro-bubbles in semi-conductor cleaning has been promoted in recent years; for example, see Japanese Unexamined Patent Application Publication No. 2008-103701. However, in the conventional cleaning apparatus using micro-bubbles, since the nozzle of the micro-bubble generating device is located in the bottom of the cleaning bath, and since the micro-bubble generating device occupies a large space in the cleaning bath, micro-bubble generating devices became obstructive to the installation of other devices, and the installation of the micro-bubble generating device took time and effort. In order to solve these problems, a cleaning apparatus in which a buffer tank apart from the cleaning bath containing the micro-bubble generating device has been disclosed. However, such a cleaning apparatus requires a larger installation space. Accordingly, an inline-disposition in which the micro-bubble generating device is disposed in a conduit for circulating a cleaning fluid in the cleaning bath is preferred, and such a cleaning apparatus having the inline-disposed micro-bubble generating device have been conventionally used.
However, if a micro-bubble generating device is installed in a narrow conduit, the micro-bubbles coalesce around the nozzle of the micro-bubble generating device, and the resultant bubble size is thus large. Particularly, in the case of the micro-bubble generating devices generating a vortex flow, the bubbles are brought together in the center of the conduit by a Coanda effect due to the vortex flow, and the bubble size is thus made larger. Accordingly, in a conventional cleaning apparatus, there was the problem that generating efficiency of the micro-bubble apparatus was decreased and the cleaning of the silicon wafer was compromised.